...

// Channel used to send events to the background thread

private BlockingQueue<ApplicationEvent> queue;

abstract public class ApplicationEvent {
   private final ApplicationEventType eventType;
}

enum ApplicationEventType {
   COMMIT,
   ACK_PARTITION_REVOKED,
   ACK_PARTITION_ASSIGNED,
   UPDATE_METADATA,
   LEAVE_GROUP,
}

BackgroundEventQueue and BackgroundEvent

// Channel used to send events to the polling thread for client side execution/notification

private BlockingQueue<BackgroundEvent> queue;

abstract public class BackgroundEvent {
   private final BackgroundEventType eventType;
}

enum ResponseEventTypeBackgroundEventType {
   ERROR,
   REVOKE_PARTITIONS,
   ASSIGN_PARTITIONS,
   FETCH_RESPONSE,
}

...

1. If subscribing to nothing, trigger unsubscribe()
2. clear the fetcher buffer
3. subscribes 
4. send metadata update

Unsubscribe

1. Send a leave group event
2. unsubscribe from the topics

Major Changes

Consumer Poll Changes

...